This application claims the priority of German application 197 41 868.6-21, filed in Germany on Sep. 23, 1997, the disclosure of which is expressly incorporated by reference herein.
The invention relates to an arrangement for operating a brake of a vehicle having at least one controllable electric motor and at least one conversion device for converting the rotational movement of the electric motor into a translational movement of one or several brake element(s) operatively connected with the conversion device.
Increasing density in road traffic requires motor vehicle systems which contribute to the driver's safety and relief. In this case, the trend in the automobile industry is in the direction of autonomous driving. Here, the driver is aided by "by-wire systems" and is relieved in many driving situations by intelligent systems. Current brake systems consist predominantly of hydraulic or pneumatic transmitting and boosting devices by means of which the driver directly defines the braking intervention of the wheel brake. In order to implement driver-independent braking interventions in the case of these systems, in addition to the necessary pressure supply, high expenditures with respect to component parts, such as valves, hydraulic cylinders, and the like, are required in order to control driver-independent braking interventions, for example, for a ranging control. For this reason, electromechanical wheel brakes were suggested which can be controlled electrically and make the use of hydraulic or pneumatic transmitting and boosting devices superfluous.
This type of an arrangement is known, for example, from German Patent Document DE 42 29 042 A1. In this arrangement, the electric motor is assigned to a brake element. The conversion device converts the rotational movement of the electric motor into a translational movement which results in a linear displacement of a driving piston. A fluid chamber is provided between the driving piston and a brake lining contact pressure piston, by means of which brake lining contact pressure piston, the brake linings are pressed against a brake disk. A brake fluid is situated in the fluid chamber.
In the case of this arrangement for operating a brake of a vehicle, it is advantageous that, in a danger situation, which arises, for example, when the electric motor is defective and can therefore not cause a return movement of the brake linings, the brake can be released by a pressure reduction in the brake fluid. However, in the case of this arrangement, it is a problem that, despite the electric controllability, it requires the use of a hydraulic system and thus requires brake fluid and therefore not only results in higher expenditures but, in particular, is also less environmentally friendly than a so-called "dry" brake, that is, a brake which requires no hydraulic fluid whatsoever.
Furthermore, from German Patent Document DE 42 07 640 A1, a friction brake, particularly a disk brake, is known for vehicles as well as a process for braking a vehicle, which has an electromagnetic friction clutch which is brought into a controllable frictional connection with a friction member, preferably the brake disk. By way of a toothed drive, the friction clutch is in a form-locking rotary engagement with a piston which can be axially adjusted by a rotating-direction-independent V-drive and which is part of an application device for brake linings assigned to the brake disk. For pressing the brake linings against the brake disk, energy is removed from the rotating vehicle wheel by means of the friction clutch and is assigned to the application device.
Although, in the case of this brake, a self-locking is impossible, it is a problem and a disadvantage of this brake that the electromagnetic friction clutch itself is subject to wear and therefore requires additional maintenance work on the brake which is connected with costs. Furthermore, by means of such a brake, only limited contact pressure forces can be generated by means of which the brake linings are pressed against the brake disk.
Furthermore, in the case of this arrangement, a very fast intermittent controlling of the brake is problematic since, in particular, a very fast releasing of the brake by means of the friction clutch and the toothed drive is not easily possible.
It is therefore an object of the invention to provide an arrangement for operating a brake of the initially mentioned type which, while its construction is compact, permits a very fast, also intermittent operating of a "dry" brake which can be controlled in a computer-aided manner. In particular, a braking intervention as well as a releasing of the brake is to be possible in a very rapid manner by means of standard electric motors.
In the case of an arrangement for operating a brake of a vehicle of the initially mentioned type, this object is achieved according to the invention in that the conversion device comprises two sloped disks which are arranged coaxially with respect to the electric motor, whose first sloped disk can be caused to carry out a rotating movement by means of a step-down gear driven by the electric motor, and whose second sloped disk, by way of roller bodies, which are arranged between the two sloped disks, is axially displaceable by a rotating movement of the first sloped disk.
As the result of the fact that the rotating movement of the electric motor is converted into a translational movement by a step-down gear and two sloped disks arranged coaxially to the electric motor, while the construction is extremely compact, a longitudinal displacement of an adjusting piston of a brake disk is advantageously achieved by means of a very high force which is obtained by a high torque of the step-down gear and the direct transmission by way of the two sloped disks onto the adjusting piston.
Purely in principle, the sloped disks can be constructed and disposed in various manners.
A very advantageous embodiment provides that the first sloped disk is part of a step-down gear. This not only eliminates additional structural elements, in particular, such an arrangement also very advantageously permits an extremely compact construction.
Particularly with respect to a construction, which is simple because it requires few parts and is therefore insusceptible to disturbances and simultaneously very compact, it is furthermore advantageously provided that the first sloped disk forms a part of a bearing which is arranged in a housing and which is used for bearing the rotatable first sloped disk in the housing.
As far as the construction of the first sloped disk is concerned, it is particularly advantageous, especially with respect to a construction which is extremely compact in the axial direction, that the first sloped disk has a step-shaped profile which, on the one hand, at least partially encloses the step-down gear in the axial direction, and, on the other hand, is used for receiving the roller body.
In this manner, while the construction of the whole conversion device is very compact, the first sloped disk simultaneously carries out several functions.
No detailed information has been supplied above concerning the roller bodies. In an advantageous embodiment, it is provided that the roller bodies are ball bodies or roll bodies.
For the simple and reliable transmission of the translational movement exercised by the second sloped disk to the brake elements in the form of brake linings, it is provided that the second sloped disk exercises an axially directed force in a rotationally uncoupled manner by way of bearings onto an adjusting element and by way of the latter onto an adjusting piston. Brake linings are arranged on the adjusting piston itself so that the axial force is also applied to these.
In order to, on the one hand, facilitate the return movement and thus the releasing of the brake by the electric motor and the conversion unit, and, on the other hand, hold the parts forming the above-described conversion unit in their position, it is advantageously provided that, by way of one or several restoring devices supported on the housing, a restoring force is applied to the adjusting element, the first and the second sloped disk and the bearing which is opposite to the force generated by the second sloped disk during a rotating movement of the first sloped disk.
The second sloped disk is preferably guided axially and radially in the housing by means of a ring.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.